feat(capabilities): dynamic mimetype discovery from wopi xml

[multiphlow]

Fixes #5742. This PR introduces dynamic mimetype discovery by parsing the WOPI discovery.xml using XPath, fallback in Capabilities is the static mimetypes array to ensure core stability.

Note: There are still some files in the code where Capabilities::MIMETYPES is used. This has to be correctly changed via dependency injection to use the new dynamic obtaining of the MIMETYPES
Furthermore a/some UnitTest(s) would also be required in DiscoveryServiceTest class.

Further on the discovery endpoint does not yet provide categories for the mimetypes.

[elzody]

Thanks for opening your first pull request here, it means a lot that you want to contribute. This change is especially welcome.

In order to get this in, it would be nice if you could address the following:

1. Resolve the @todo notes still left in the code
2. Add some tests to ensure the MIME types from the discovery XML are parsed correctly
3. Adjust the currently failing tests as the failures seem to be related to this change

If you need help with any of those, please feel free to reach out; I'm more than happy to assist!

[juliusknorr]

Cypress and integration tests seem to be not running properly with the branch being on a fork, so they are fine to ignore for now.

Actually the cypress failures seem indeed related and seem to tigger a javascript error:

  8) Open existing office files
       Notebookbar UI: Open drawing.odg the viewer on file click:
     Error: The following error originated from your application code, not from Cypress.

  > Handler needs a valid mime array or mimesAliases

When Cypress detects uncaught errors originating from your application it will automatically fail the current test.

This behavior is configurable, and you can choose to turn this off by listening to the `uncaught:exception` event.

https://on.cypress.io/uncaught-exception-from-application
      at validateHandler (http://172.17.0.1:8081/apps/richdocuments/js/richdocuments-init-viewer.js?v=f5f31c4f-0:191:15)
      at registerHandler (http://172.17.0.1:8081/apps/richdocuments/js/richdocuments-init-viewer.js?v=f5f31c4f-0:170:5)
      at <unknown> (http://172.17.0.1:8081/apps/richdocuments/js/richdocuments-init-viewer.js?v=f5f31c4f-0:488:67)
      at <unknown> (http://172.17.0.1:8081/apps/richdocuments/js/richdocuments-init-viewer.js?v=f5f31c4f-0:489:3)
      at <unknown> (http://172.17.0.1:8081/apps/richdocuments/js/richdocuments-init-viewer.js?v=f5f31c4f-0:491:12)

[multiphlow]

@juliusknorr A while ago I fixed the issue with array_unique.
@elzody For now this is ok, since it is a first coding task ;)

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